My best friend dated a chick for a year or so. Me and him ended up being good friends with the family, went to their house randomly for dinners and such (her dad was a head chef at one of the nicer restaurants downtown).
When my buddy dated Megan, her sister was about 13 or so.
Went home for leave the last year I was active duty, Megan's sister Lori was 16, I was 23 or so. She stared at me so much and hung out in the same room that I was in that my friends, her sisters, and I were all uncomfortable as hell. I was even more uncomfortable because she was so fucking hot. The creepiest thing about it was that her mom was so extraordinarily happy about it.
By the time she was eligible, she was knocked up by a high school boyfriend. The next time I saw her after that, her baby was about 4 months old, and her post-pregnancy tits were god damned huge and beautiful. And I was dating someone.
I have a picture somewhere of her boobs in a very flattering dress. When I get back from physical therapy I will look for it.
Bolded for added lols
So you were creeped out, but not creeped out enough.